The magnetic properties of thin film magnetic recording layers must be tightly controlled in order for the magnetic media, such as a rigid or hard recording disk, to be useful in the high density storage of digital data such as is used in conventional data processing installations.
Exemplary magnetic properties of thin film magnetic recording layers, such as are used to describe the hysteresis loop of a magnetic material, are the coercivity (H.sub.c), the remanence (M.sub.r), the remanence thickness product (M.sub.r T), the squareness (S), and the coercive squareness (S.sup.*).
A goal in the fabrication or manufacture of thin film magnetic recording media is to obtain bulk magnetic properties that are compatible with, and indeed are required by, the read/write transducing head of the data processing unit in which the media will be used. For example, the coercivity of a magnetic film is an effective measure of the magnetic field that is required from a transducing head in order to reverse the magnetization direction within the magnetic film.
A number of means have been practiced in the art to control the magnetic properties of thin film magnetic media. Examples are the use of different materials directly under the thin film magnetic layer (i.e. the use of an underlayer), variation in the thickness of the magnetic layer, and the use of different magnetic alloys in the magnetic layer. However, the art has generally not succeeded in controlling the bulk magnetic properties of thin film magnetic layers when a nonvariable set of material and thickness requirements are specified for the magnetic layer. A possible exception to this has been the use of variable preheating of the disk substrate. However, this preheating step may lead to other inconsistencies relative to magnetic remanence and/or warping of the disk.
U.S. Pat. No. 4,749,459, incorporated herein by reference, describes a number of ways by which the coercivity of a thin film magnetic recording layer may be controlled, including forming the magnetic film on a chromium underlayer and controlling the magnetic film's coercivity by controlling the thickness of the underlayer, controlling the amount of platinum in the magnetic layer, and sputter depositing the magnetic layer in an atmosphere that includes argon and a trace amount of a selected gas such as nitrogen, ammonia, or oxygen and nitrogen. U.S. Pat. Nos. 4,231,816, 4,640,775 and 4,803,130 describe the sputtering of metal alloys in an atmosphere containing a selected gas, including nitrogen.
While the various means practiced in the art for controlling the magnetic properties of thin film magnetic media have been generally useful, there remains a need in the art for a simple means whereby the magnetic properties of a thin film recording layer can be controlled in a manner that provides a great deal of disk manufacturing process latitude, independent of controlling parameters such as the thickness of the thin film magnetic layer.